A group of Iranian military operatives and missile technology experts are taking part in a test launch of a long-range ballistic missile in North Korea Sunday, Reuters reported.

The Iranians have been active in North Korea since late October, the agency reported, citing a Western official quoted by the Kyodo News Agency of Japan.

The group is reportedly based at a military base about 85 kilometers from the Chinese border and is assisting in missile and nuclear technology development for the North Korean military. Iran and North Korea signed a technology and science cooperation agreement in early September, and according to Reuters, US officials believe that Iran acquired ballistic missile parts from North Korea in 2010.

On Saturday, Pyongyang announced plans to test-fire a long-range rocket sometime between December 10 and 22. It would be North Korea’s second launch attempt under leader Kim Jong Un, who took power following his father Kim Jong Il’s death nearly a year ago. Some analysts have expressed skepticism that North Korea has corrected whatever caused the embarrassing misfire of its last rocket eight months ago. That launch earned the country widespread international condemnation.

North Korea has capable short- and medium-range missiles, but long-range launches in 1998, 2006, 2009 and in April of this year ended in failure. North Korea is not known to have succeeded in mounting an atomic bomb on a missile but is believed to have enough weaponized plutonium for at least half a dozen bombs, according to US experts. In 2010 it revealed a uranium enrichment program that could provide a second source of material for nuclear weapons.

North Korea under its young leader has pledged to bolster its nuclear arsenal unless Washington scraps what it calls a “hostile” policy. North Korea maintains that it is building bombs to defend itself against what it sees as a US nuclear threat in the region.